Particles for electrophoretic media

Abstract

Compositions of encapsulated triboelectrically charged particles and methods for making them using a spinning disc process are disclosed. The methods can be used to make charged pigment particles embedded in a neutral polymer matrix. The polymer matrix keeps oppositely charged pigment particle from agglomerating. The particles can be used for electrophoretic displays.

1 . A composition comprising.
 one or more triboelectrically charged pigment particles dispersed and embedded within a polymer matrix,
 wherein the polymeric matrix includes an additive that improves the tribocharging characteristics of the pigment. 
   
     
     
         2 . The composition of  claim 1  wherein the polymer matrix comprises a melt having a viscosity of less than about 50 centipoise. 
     
     
         3 . The composition of  claim 1  wherein the polymer matrix comprises a melt having a viscosity of between about 5 to about 50 centipoise. 
     
     
         4 . The composition of  claim 1  wherein the polymer matrix comprises a wax selected from the group consisting of a thermoplastic a synthetic microcrystalline wax, a crystalline polyethylene wax, and other wax-like materials having a melting point from about 50° C. to about 200° C. and a sharp melting or crystallization temperature of less than about 5° C. 
     
     
         5 . The composition of  claim 1  wherein the additive comprises an oxide. 
     
     
         6 . The composition of  claim 1  wherein the additive comprises an acetate ester of a copolymer of polyethylene and polyethylene oxide. 
     
     
         7 . The composition of  claim 1  wherein the pigment particles comprise spherically shaped particles. 
     
     
         8 . The composition of  claim 1  wherein the pigment particles comprise one or more of the following: TiO 2 , ZrO 2 , ZnO, Al 2 O 3 , BaSO 4 , and CaCO 3 . 
     
     
         9 . The composition of  claim 1  wherein the pigment particles comprise one or more of the following: an organic pigment and an organometallic. 
     
     
         10 . The composition of  claim 1  wherein the particles are used in an electrophoretic display device. 
     
     
         11 . The composition of  claim 1  wherein the particles have an electrophoretic mobility and density for use in an electrochromic display. 
     
     
         12 . The composition of  claim 1  further including a dielectric fluid. 
     
     
         13 . The composition of  claim 1  wherein the composition comprises at least two groups of particles having different electrophoretic properties. 
     
     
         14 . The composition of  claim 13  where the particles are buoyant and suspended without settling in the fluid. 
     
     
         15 . A composition comprising:
 one or more triboelectrically charged pigment particles dispersed and embedded within a polymer matrix,
 wherein the polymeric matrix includes an additive that improves the tribocharging characteristics of the pigment; and 
 wherein the additive comprises an acetate ester of a copolymer of polyethylene and polyethylene oxide, and 
   the composition further including a dielectric fluid where the particles are buoyant and suspended without settling in the fluid.   
     
     
         16 . The composition of  claim 15  wherein the pigment particles comprise one or more of the following: TiO 2  ZrO 2 , ZnO, Al 2 O 3 , BaSO 4 , and CaCO 3 . 
     
     
         17 . The composition of  claim 15  wherein the pigment particles comprise one or more of the following: an organic pigment and an organometallic. 
     
     
         18 . A composition comprising:
 one or more triboelectrically charged pigment particles dispersed and embedded within a polymer matrix,
 wherein the polymeric matrix includes an additive that improves the tribocharging characteristics of the pigment; and 
 wherein the additive comprises an oxide, and 
   the composition further including a dielectric fluid where the particles are buoyant and suspended without settling in the fluid.